1. Field of the Invention
The present invention relates to a mobile communication terminal. More particularly, the present invention relates to a dome switch assembly that can reduce the Specific Absorption Rate (SAR) value and improve radiation emission performance of a mobile communication terminal, and to a mobile communication terminal using the dome switch assembly.
2. Description of the Related Art
When mobile communication terminals are used to communicate with a network, they emit low levels of radio frequency (RF) electromagnetic waves. There are concerns that the emitted RF electromagnetic waves may be harmful to a human body. SAR values are used to gauge the exposure of user to RF electromagnetic values generated by a mobile communication terminal. SAR stands for Specific Absorption Rate, and is a unit of measurement for the amount of RF electromagnetic waves absorbed into a human body when using a mobile communication terminal.
Higher SAR values indicate that more RF electromagnetic waves are being absorbed into a human body. Since the RF electromagnetic waves may have adverse effects on a human body if too many are absorbed, most countries set acceptable maximum SAR values, particularly for the head. Currently, maximum acceptable SAR values are 1.6 W/kg in South Korea, the U.S.A., Australia and Canada, and 2.0 W/kg in Europe and Japan. In South Korea, all mobile communication terminals introduced into the market since December, 2002 include a disclosure of the meaning and value of SAR and its influence on the human body.
SAR values have a close relationship with the near field of RF electromagnetic waves radiated by an antenna of a mobile communication terminal. Therefore, SAR values are related to the transmission power of the mobile communication terminal, the antenna characteristics, the type of device, and similar factors. Thus, to reduce SAR values, conventional methods of using a directional antenna, intercepting RF electromagnetic waves by attaching a separate interception plate, and inserting an electric wave absorber are used.
The method of using a directional antenna to reduce SAR values requires a very complicated structure, however, and is incompatible with the current market trend of reducing the thickness and size of mobile terminals. The methods of using a separate interception plate and inserting an electric wave absorber have different effects depending on the material characteristics and the position where the devices are attached, and the manufacturing processes are also complicated.
To address such problems, as shown in FIGS. 1 and 2, a method of reducing the SAR value of a mobile terminal by connecting a ground layer 36 of a dome switch assembly 30 with a hinge 60 has been used.
Referring to FIGS. 1 and 2, a conventional folding type mobile communication terminal 100 includes a main body 10, a cover 50, and a hinge 60. The main body 10 includes a dome switch assembly 30 provided under a keypad 40. The cover 50 includes a display window 51 provided in a surface facing the upper surface of the main body 10. The hinge 60 connects the ends of the main body 10 and the cover 50 so that the cover 50 may be opened and closed with respect to the main body 10.
The dome switch assembly 30 is provided on an upper surface of a printed circuit board (PCB) 20 located within the main body 10. The dome switch assembly 30 is activated by keys on the keypad 40. The dome switch assembly 30 has a structure in which dome switches 35 and a ground layer 36 are formed on an upper surface of an insulating base film 31. The ground layer 36 is disposed apart from the dome switch 35 on the upper surface of the base film 31. A hinge contact unit 38 extends from an external side surface of the ground layer 36 adjacent to the hinge 60 to contact the hinge 60. The ground layer 36 is grounded with the PCB 20.
Therefore, the ground layer 36 of the dome switch assembly 30 performs the function of an interception plate and an electric wave absorber, so that the SAR value of the mobile terminal can be reduced to some extent without requiring a separate interception plate or electric wave absorber.
Since the hinge contact unit 38 protrudes from the external side surface of the ground layer 36 to contact the hinge 60, the ability to adjust the position and length of the hinge contact unit 38 is limited. Accordingly, there is a limitation on the amount of SAR reduction or radiation emission improvement that can be accomplished by the hinge contact unit 38, and there is a need for an improved dome switch assembly and mobile communication terminal having the same which reduces SAR values and radiation emission.